This invention relates to an ignition timing controller for a gasoline engine on an automobile and the like.
In a known gasoline engine for an automobile or the like, when a throttle valve in a carburetor is opened to such an extent that its upper edge is rotated slightly above an advancer port opening to the carburetor, the negative pressure prevailing behind the throttle valve is transmitted through the advancer port into a negative pressure chamber of a vacuum advancer which controls the timing for distribution of igniting voltage by a distributor, and ignition timing is advanced, whereby combustion of a fuel-air mixture in engine cylinders is improved and consequently good engine performance is maintained. The improvement of combustion, however, results in rise of combustion temperature, causing in some cases generation of NOx (nitrogen oxides) as the result of a reaction between N.sub.2 and O.sub.2 in fuel gas. Emission of NOx must be controlled in order to purify exhaust gas; therefore, in some operation range of an engine, it is necessary to retard ignition timing or decrease the distributor advance angle in order to reduce NOx or HC (hydrocarbons).